This invention relates to electrophoretic display panel apparatus and methods therefor and more particularly electrophoretic display panel apparatus having improved contrast and image alignment.
In U.S. patent application Ser. No. 670,571 entitled "Electrophoretic Display Panels And Associated Methods" as filed on Nov. 13, 1984 in the names of Frank J. DiSanto and Denis A. Krusos and assigned to the assignee of the instant application there is disclosed an electrophoretic display panel capable of exhibiting resolution characteristics of 200 lines per inch. This display panel is typically configured as an 81/2.times.11 flat panel having a depth of less than 2 inches. Such a panel is highly advantageous in that the resolution displayed thereby equals or exceeds many CRT's, the display exhibits hysteresis so that it need not be constantly refreshed or maintained in an energized condition and the reflective characteristics thereof readily accommodate xerographic printing or hard document production techniques.
Since the depth of such a panel is quite small when compared to standard CRT display devices, it will be seen that the same completely alleviates the space problems associated with conventional personal computer, display terminal or work station installations where the size of the CRT display is often the largest item involved especially when it is considered that hardware elements such as printers and CPU's may often be remotely located. Thus, such a flat panel display occupies little more space than a picture frame or typing stand so that the same may readily be incorporated into existing work stations or desk areas without overwhelming the work area. Furthermore, if such a display is hinged to a document location input of a xerographic copier or the like, silent printing stations may be achieved without any specialized input or writing section therefor such as now conventionally provided by laser printers and the like. The provision of separate panel displays near an operator and at a copier also facilitates the creation of silent, attractive word processing or data processing installations which are small in size so that the same may be readily incorporated into pre-existing work areas.
As described in greater detail in the above-identified patent application, the electrophoretic display described therein generally takes the form of a wafer structure formed on a glass sheets generally slightly larger than the size of the panel. The glass sheet is coated with indium-tin oxide (ITO) having a horizontal cathode line pattern etched therein to form horizontal row conductors. In the case of an 81/2.times.11 inch panel having a resolution of 200 lines per inch there will be 2,200 horizontal rows of conductors forming the horizontal cathode line pattern. Since the ITO layer is very thin those of ordinary skill in the art will appreciate that it is relatively transparent. An insulating layer formed by photoresist such as phenolic resin impregnated with photoactive material is deposited over the cathode line structure. Thereafter, the photoresist material is overcoated with a nickel layer through the use of sputtering techniques or the like and then the nickel is overcoated by another thin layer of photoresist material.
Once the solid nickel layer sandwiched by solid layers of photoresist material is formed over the horizontal cathode rows formed in the ITO, a mask having vertically disposed column conductors is placed on the top layer of photoresist and thereafter the wafer formed is exposed to ultraviolet light and developed. Where the photoresist material has been exposed to ultraviolet light the same will be removed leaving vertically disposed columns of photoresist overcoating the nickel layer together with adjacent vertical columns of nickel from which the photoresist has been removed. The nickel is then etched so that nickel material which is not overcoated by photoresist is removed. Subsequently, the wafer structure is flooded with ultraviolet light and again developed so that the vertical layers of photoresist overlying the remaining vertical strips of nickel are removed. Once this is done the wafer is placed in a plasma etcher which effectively removes all photoresist material which is not overcoated by nickel so that columns of vertically disposed nickel conductors which act as grids in the triode structure being formed remain. If a panel display having dimensions of 81/2.times.11 inch and a resolution of 200 lines per inch is again considered it will be appreciated that 1,700 vertical columns consisting of 1,700 grid lines are required.
Because the electrophoretic phenomena employs what is in effect the migration of pigment particles, early attempts at creating such devices sought to control migration about the cathode or the intersection of the cathode and grid conductors to form a display. Thus, typically pigment particles would migrate toward and away from the intersection of the cathode and grid conductors to form display elements about the periphery of such intersections it being noted that while cathode conductors such as the row conductors here described would typically be sufficiently thin to be transparent grid conductors could not be made to change color. Further efforts to improve the manner in which grid conductors would control the migration of pigment particles involved an aperturing of such grid conductors as disclosed in U.S. patent application Ser. No. 670,571, as aforesaid, and shown for instance in U.S. Pat. No. 4,203,106 which issued to Daliasa et al. on May 13, 1980 and is assigned to North American Phillips Corporation. When the grid structure is apertured much greater control of the voltage gradient at locations where the pigment particles and the grid interact is available and under these conditions contrast and resolution may be enhanced.
An aperturing of the grid conductors, however, is quite difficult becuse while photoetching or engraving techniques such as described above are eminently well suited and capable of causing straight line segments which can be extremely thin to be formed, the same do not work especially well when it is desired to form apertured conductor lengths or the like. Furthermore, when such conductors are apertured only in the area of the intersection with the cathode row conductors any misalignment in the area of the intersection will result in a substantial loss of the voltage gradient control characteristics being sought. Such a situation, it will be appreciated, can be a great problem where the electrophoretic display panel being formed is configured to correspond in size to a normal page such as here indicated as comprising an 81/2.times.11 inch display and exhibits high resolution characteristics such as a 200 line per inch level described in U.S. patent application Ser. No. 670,571. In such a display it will be recalled 2,200 horizontal row conductors and 1,700 vertical column conductors are employed in forming the cathode grid matrix and hence appropriate alignment at the 3,740,000 intersections which result can be a substantial problem.
Once the vertically disposed grid structures are formed in the column direction, the electrophoretic panel is completed by forming an enclosing anode structure which may typically be formed of ITO in such manner as described in connection with U.S. patent application Ser. No. 670,571. The anode structure encloses the cathode-grid structure described above and provides an area in which a fluid containing appropriate electrophoretic pigment particles which have been charged may be enclosed. Thereafter, charged pigment particles dispersed in a dielectric fluid to form an electrophoretic dispersion are inserted into the cell and the resulting structure is enclosed within a frame or the like through which electrical connection to the individual grid and cathode conductors is provided.
In the case of the 81/2.times.11 inch electrophoretic panel display described above such a frame structure must typically provide individual connection to 2,200 cathode lines and 1,700 grid lines although, as will be apparent to those of ordinary skill in the art, a converse allocation may be employed. Because so many tiny conductors are involved, it is advantageous to provide adjacent conductors in each column and row with contact or connection pads brought out to the periphery of the panel in such a manner that adjacent conductors are brought out to opposite sides of the panel in an interleaved fashion. Thus typically, odd numbered row conductors are brought out to the right while even numbered row conductors are brought out to the left. In similar fashion odd numbered column conductors are brought out to the top while even numbered column conductors are brought out to the bottom. This effectively doubles the space available for a connection. Complementary connection pads are provided within the frame employed to house the panel and provide electrical connection thereto. Interconnection of pads on the frame and on the panel may be conveniently supplied through the use of Zebra strips or the like as the same readily avoids shorting.
Even under conditions where only half the row and column conductors are brought out to each side and the top and bottom of the panel being formed, it will be seen that under the conditions set forth above 1,100 row conductors are present on each side of the panel while 850 column conductor pads are present at the top and bottom portions of the panel. These in turn must be connected to an equal number of corresponding located connector pads in the frame. If it is assumed that an unreasonable amount of area is not to be provided for location of this large number of connector pads about the periphery, it will be seen that the connector pads involved cannot be extremely large and in actual devices tend to be approximately 0.375 inches by 0.005 inches. Thus, when the display panel is inserted into the frame it is not unusual that misalignment between connecting pads occurs so that, for example, the connector pad in the frame associated with row 3 is connected for example to the connector pad on the panel associated with row 1 or the like. This, it will be appreciated, will result in substantial misalignment of the image information being formed on an operating display as in effect, information intended to be written on row 3 of the display is effectively written into row 1 and row 1 information is omitted. Furthermore, since the display panel and mounting frame are typically rectangular, misalignment on a given side will frequently result in misalignment on the top and bottom so that effectively image rotation will occur.
While misalignment problems of the foregoing type may sometimes be minimized through the use of very tight manufacturing tolerances on the panel and frame together with the inclusion of locating pins or, alternatively, etching or painting indicia on the panel and frame and providing an assembly fixture, such solutions results in an untoward increase in manufacturing costs and are frequently not usable under condictions of field replacement or repair. Thus, to maintain very tight manufacturing tolerances on the panel and frame and including locating pins therein will result in mated pairs which are extremely costly to produce and would preclude a replacement of only an individual frame or panel in the field. Similarly, etching or painting indicia on the panel and frame and providing an assembly fixture therefor would impose a requirement that such fixture include precise optics to perform the required alignment so that such a fixture could not be utilized in the field and would be disproportionately costly in a manufacturing environment.
Accordingly, from the foregoing, it will be recognized that if practical and commercially viable electrophoretic display panels are to become a significant factor in the marketplace, alignment problems associated both with the structure of the grid electrodes in triode forms of these devices and with the mounting of the resulting panel formed into a housing to supply column and row information thereot must be solved. In addition, even with devices exhibiting extremely high resolution such as the 200 line per inch resolution described above, techniques for optimizing contrast must be developed.
Therefore, it is a principle object of the present invention to provide electrophoretic display panel apparatus having improved alignment characteristics and methods therefor.
A further object of this invention is to provide electrophoretic display panel apparatus have improved contrast characteristics and methods for allowing the contrast exhibited by such panels to be optimized.
An additional object of the present invention is to provide electrophoretic display panel apparatus and methods therefor wherein individual grid electrode structure is tinted in appearance and permits the formation of reservoirs for electrophoretic particles intermediate such tines.
A further object of the present invention is to provide electrophoretic display panel apparatus having an adjustable delay line structure which is operable to correct misalignment of the panel within a mounting frame or the like.
Another object of the present invention is to provide electrophoretic display panel apparatus and methods therefore wherein each grid electrode includes a plurality of parallel conductors in the form of tines so that appropriate intersections with cathode conductors will occur even if minor misalignment between an array of row conductors in the form of cathodes and an array of grid electrodes occurs.
An additional object of the instant invention is to provide electrophoretic display panel appartus and methods therefor wherein the grid electrodes take the form of a plurality of parallel tines each tine having width characteristics which may selectively vary to optimize contrast conditions exhibited by the display apparatus.
Various other objects and advantages of the present invention will become clear from the following detailed description of an exemplary embodiment thereof and the novel features will be particularly pointed out in conjunction with the claims appended hereto.